We haven't yet found evidence of life outside of Earth - but then again, we've not really been able to look all that hard. We'd probably know if there were a t

We haven't yet found evidence of life outside of Earth - but then again, we've not really been able to look all that hard. We'd probably know if there were a technologically advanced civilization around in the area immediate around Sol, at approximately the same time as today. That area isn't all that large due to the inverse square law; even if a species were actively trying to communicate with us via RF, it would be indistinguishable from the background quickly relative to astronomical distances. We'd probably know (or know soon) if large-scale biological processes were happening near us, from the signatures of the chemicals that are the hallmarks of biology as we know it. That we've found neither of those means we can't prove life exists elsewhere, but does _not_ prove that it doesn't. That said, if abiogenesis were a common phenomenon, wouldn't we expect it to have arisen multiple times on Earth? The fact that we've not found any life that doesn't rely on DNA means is strong evidence of one of two things: either all life must have DNA, or life only arose on Earth once. If life requires DNA... then where did DNA come from? We're back to square one. If life only arose on Earth once, that's weak evidence that abiogenesis isn't common. By extension, it's weak evidence against panspermia.